V. J. Logeeswaran

Micromachined in-plane vibrating diffraction grating laser scanner

In this letter, we present a novel micromachined vibrating diffraction-grating laser scanner that utilizes in-plane angular vibration of a planar diffraction grating causing the diffracted laser beam to scan. The proposed micromachined diffraction-grating laser scanner can operate with low voltage and has the potential to scan at high frequencies without the optical performance degradation due to dynamic nonrigid-body deformation, which is prevalent in conventional high-speed out-of-plane torsional micromirror scanners. A prototype grating scanner has been developed using micromachining technology to demonstrate this new microscanner principle. The tested device is capable of scanning an optical angle of 15.9/spl deg/ with virtually bow-free scan-line at a resonant frequency of 8.34 kHz for a 635-nm wavelength incident laser beam, electrostatically driven by 15-V dc bias and 15-V ac voltages.

A differential capacitive low-g microaccelerometer with mg resolution

Abstract A low-cost differential capacitive accelerometer with a resolution of 5 m g (1 g =9.81 m/s 2 ) and high sensitivity (800 mV/ g ) has been designed with a full measurement range of ±2 g . By using the single crystal reactive ion etching and metallisation (SCREAM) process, beams with high aspect ratio, small air gap for large capacitance variation and low parasitic capacitance have been attained. The fabricated microaccelerometer also offers high output and it has successfully survived a shock of 1000 g . The effects of electrostatic spring constant on the natural frequency and sensitivity of the accelerometer have been thoroughly discussed, and obliqueness of the beams has also been taken into consideration. The ratiometric error has been studied, and is well below 2% with a cross axis sensitivity of less than 3%. The operating voltage is 5 V DC. The construction is based on a two-chip design and the sensing element is connected to a CMOS ASIC by wire bonding.

First Harmonic (2 f ) Characterisation of Resonant Frequency and Q-Factor of Micromechanical Transducers

In this paper, the response to the first harmonic component (2f) of the electrostatic force in single terminal driven electrostatic comb-drive and parallel-plate drive was used as a signal to extract device parameters, namely, the Q-factor and resonant frequency instead of the fundamental (1f) resonance response. It is shown that the difficulty in motional measurement due to electrical cross-talk (parasitics) using 1f measurement can be overcome with a higher signal-to-noise ratio of the 2f signal. Both atmospheric (low-Q) and reduced pressure environment were investigated using off-chip electronics and lock-in amplifier. The measurements were done on the electrostatic comb-drive and capacitive parallel plate sensing plates that form the two core modules of a yaw rate sensor (dual-axis resonator). The effects of AC and DC bias voltages on the measured response have been investigated. Experimental amplitude and phase response data have been analysed using the Lorentzian curve-fit, Resonance Curve Area (RCA) method, the half-power bandwidth method (3 dB) and the Nyquist plot for data fitting and determination of the Q-factor and resonance frequency.

Efficient design of micromechanical gyroscopes

We consider a general approach to the analysis of the dynamics and errors of different types of micromechanical vibratory gyroscopes, as well as calculation of their performances for application in the design of such gyroscopes. Specifically, we investigate and analyse the dynamics and errors of single-mass gyroscopes, for both translational and rotational movement of the sensitive element. Based on the generalized motion equations, we derive and analyse analytical dependences for basic errors, such as scale factor nonlinearity, bias from misalignment between elastic and measurement axes, and bias from vibrations and dynamic error caused by harmonic angular rate. As a result of dynamics and errors analysis, formulae for the calculation of the main performances are derived, as well as optimal sensitive element design methodologies.

Micromechanical digital-to-analog converter for out-of-plane motion

This paper describes a novel micromechanical digital-to-analog converter (MDAC) for out-of-plane motion using electrostatic parallel-plate actuators. The proposed mechanism converts an N-bit digital signal to a mechanical out-of-plane displacement that is proportional to the analog value represented by the N-bit binary word. The mechanism is analogous to that of an electrical binary-weighted-input digital-to-analog converter (DAC). It consists of a movable platform, an array of parallel-plate microactuators each operating in an ON/OFF mode and a set of connection springs that connect the actuators to the platform. The spring constants of the connection springs are weighted so that the stiffness of successive springs is related by a factor of 2. A 4-bit mechanism has been fabricated using the Poly-MUMPS process, achieving a total stroke of 675 nm (full-scale output) and step size (LSB) of 45 nm in a highly repeatable and stable manner. The linearity error (LE) of the device is within /spl plusmn/0.28 LSB, and the differential linearity error (DLE) is within /spl plusmn/0.25 LSB. This mechanism can be configured for many promising applications, particularly in optical devices and systems such as tunable external cavity diode laser, tunable VCSELs, adaptive micromirror array and tunable wavelength filter.

Design and fabrication of a micromachined resonant gyroscope

The micromachined gyroscope is rapidly gaining popularity as a rate sensor for application in areas such as automotive and aerospace systems, where low power consumption, high sensitivity, low temperature drift and good stability are prerequisites. In this paper, the overall design and fabrication process of a reactive ion-etched inertial resonant gyroscope based on the capacitive sensing principle is reported. The experimental results are also discussed.

2f method for the measurement of resonant frequency and Q-factor of micromechanical transducers

In this paper, the response to the first harmonic component (2f) of the electrostatic force in single terminal driven electrostatic comb-drive and parallel-plate drive was used as a signal to extract device parameters, namely, the Q- factor and resonant frequency instead of the fundamental (1f) resonance response. It is shown that the difficulty in motional measurement due to electrical cross-talk (parasitics) using 1f measurement can be overcome with a higher signal-to-noise ratio of the 2f signal. Both atmospheric (low-Q) and reduced pressure environment were investigated using off-chip electronics and lock-in amplifier. The measurements were done on the electrostatic comb-drive and capacitive parallel plate sensing plates that form the two core modules of a yaw rate sensor (dual-axis resonator). The effects of AC and DC bias voltages on the measured response have been investigated. Experimental amplitude and phase response data have been analyzed using the Lorentzian curve-fit, Resonance Curve Area (RCA) method, the half-power bandwidth method (3dB) and the Nyquist plot for data fitting and determination of the Q-factor and resonance frequency.

Diffraction grating scanner using a micromachined resonator

We present a micromachined resonant diffraction grating laser scanner that utilizes in-plane angular vibration of a planar diffraction grating causing the diffracted laser beam to scan. The scanner consists of an electrostatic comb-drive microresonator and a diffraction grating plate having a grating period of 4 /spl mu/m. The proposed micromachined diffraction grating laser scanner has the potential to scan at high frequencies without the optical performance degradation due to dynamic non-rigid-body deformation compared to out-of-plane micromirror scanners. A prototype grating scanner has been fabricated using the Poly-MUMPS process. It is capable of scanning optical angles of 1.31/spl deg/(1/sup st/-order), 2.13/spl deg/(2/sup nd/-order) and 3.42/spl deg/(3/sup rd/-order) at a resonant frequency of 7.67 kHz for a 635-nm-wavelength incident laser beam, when driven by the electrostatic comb-drive push-pull mechanism with 20 V DC bias and 20 V p-p AC voltages. The scanning angle of the device can be significantly increased by reducing the grating period to sub-wavelength level.

Line-addressable digital-deflection programmable micromirror array

We report a novel digital-deflection programmable micromirror array driven by micromechanical digital-to-analog converters that eliminates the need for electrical digital-to-analog converters for analog displacement control, thus simplifying the driving circuitry and reducing the overall system cost. Furthermore, owing to the bistable and hysteretic characteristics of parallel-plate electrostatic actuators, an array of micromirrors can be controlled by means of row- and column-addressing lines, which drastically reduce the number of routing wires and allow array sizes to increase while they maintain high array quality.

Micromechanical torsional digital-to-analog converter for open-loop angular positioning applications

This paper reports a novel micromechanical torsional digital-to-analog converter (MTDAC), operated in open-loop with digitally controlled precise multi-level tilt angles. The MTDAC mechanism presented is analogous to that of an electrical binary-weighted-input digital-to-analog converter (DAC). It consists of a rigid tunable platform, an array of torsional microactuators, each operating in a two-state (on/off) mode, and a set of connection beams with binary-weighted torsional stiffnesses that connect the actuators to the platform. The feasibility of the proposed MTDAC mechanism was verified numerically by finite element simulations and experimentally with a commercial optical phase-shifting interferometric system. A prototype 2-bit MTDAC was implemented using the poly-MUMPS process achieving a full-scale output tilt angle of 1.92° with a rotation step of 0.64°. This mechanism can be configured for many promising applications, particularly in beam steering-based OXC switches.